Conventional turbine and turbofan engines for aircraft include a plurality of fan blades that rotate within a duct commonly known as a fan case. The fan case serves as a protective covering to protect the fan blades and the aircraft. Further, the fan case channels airflow into the turbine engine. The inner surface of the fan case is constructed to withstand impacts from objects that may come into contact with the fan case, broken fan blades and includes acoustical features to reduce noise emitted from the engine.
The acoustical features include a layer of noise attenuation structures covered by a protective face layer including a plurality of openings. The face layer is typically a thin sheet of metal or composite material mounted over the noise attenuation structure. Noise causing pressure disturbances emanate through the openings within the face layer into the noise attenuation structure where the pressure disturbances dissipate to reduce the total amount of noise.
Water may leak into the fan casing through the face layer and the noise attenuation structure.